Approved Final TMDLs

Final TMDLs Approved by EPA: Potomac River Montgomery County

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The Potomac River Montgomery County watershed consists of the mainstem Potomac River within Montgomery County, Maryland, and all of the tributaries draining to this stretch of the mainstem Potomac, except for Seneca Creek and Cabin John Creek. The Montgomery County portion of the mainstem Potomac River flows 39 miles from the Frederick/Montgomery County border down to the Montgomery County/Washington DC border. The actual watershed is located predominately in Montgomery County, Maryland, covering 140.0 square miles, but small portions of the watershed also extend into Frederick County, Maryland (0.7 square miles), and Washington, DC (2.1 square miles). The primary tributaries draining to the mainstem Potomac River within the watershed include the Little Monocacy River, Broad Run, Horsepen Branch, Muddy Branch, Watts Branch, Rock Run, and Little Falls Branch. Several areas within the watershed are highly developed and include parts of the towns of Gaithersburg, Rockville, Bethesda, and Chevy Chase.

MDE has identified the waters of the MD 8-digit Potomac River Montgomery County watershed on the State’s Integrated Report as impaired by nutrients – phosphorus (1996), sediments (1996), bacteria - mainstem only (2002), impacts to biological communities (2006), and polychlorinated biphenyls (PCBs) in fish tissue (2008). The designated use of the MD 8-digit Potomac River Montgomery County mainstem and its tributaries is Use I-P (Water Contact Recreation, Protection of Aquatic Life, and Public Water Supply).

The TMDL, available below, addresses the 1996 sediments listing, for which a data solicitation was conducted, and all readily available data from the past five years were considered. The TMDLs set the maximum load limit for sediments, and provides load allocations to point and nonpoint sources. The MD 8-digit watershed was delisted for bacteria in 2004, and a Water Quality Analysis (WQA) for eutrophication to address the nutrients/phosphorus listing is scheduled to approved by the EPA in 2012. In the 2012 Integrated Report, the listing for impacts to biological communities includes the results of a stressor identification analysis, and the PCBs in fish tissue listing will be addressed at a future date.

Total Maximum Daily Load of Sediment in the Potomac River Montgomery County Watershed, Montgomery and Frederick Counties, Maryland